This article addresses how to distinguish mathematical arguments created during whole class discussions in grades 3-5 in Sweden, while taking a broad range of communicational resources, such as speech, drawings and symbols, into account. We present a step-by-step framework of how to systematically reconstruct mathematical arguments. The framework is developed drawing on Toulmin's model of argumentation and a multimodal approach. When giving account for the framework, we show how various communicational resources convey the mathematical meaning of the arguments created. The framework can be used for further research investigating interaction in classroom settings, for teacher students as a basis for reflection during practicum periods, as well as a lens for teachers in identifying informal and formal mathematical arguments in day-to-day communication in the mathematics classroom.